


How to solve C++ syntax error: 'expected primary-expression before ';' token'?
Aug 25, 2023 pm 09:34 PMHow to solve C syntax error: 'expected primary-expression before ';' token'
When learning and writing C code, we often encounter various syntaxes mistake. One of the common errors is 'expected primary-expression before ';' token'. This error often occurs when a semicolon is used to end a statement, but the structure of the statement is incorrect. This article details the cause of this error and provides a solution.
There are usually two reasons for this error: the variable is not defined correctly or the wrong syntax structure is used. Below we will explain these two situations respectively and provide corresponding solutions.
Situation 1: Incorrectly defined variables
When we reference an incorrectly defined variable in C code, the compiler will report an error 'expected primary-expression before ';' token '. This usually happens in the following situations:
- Improper declaration of variable type: In C, we need to declare the type of the variable before using it. If we forget to define the type of a variable before using it, it will result in a compilation error. For example:
x = 5;
In the above code, the type of variable x is not defined, and the compiler will report an error.
Solution: Declare the type of the variable correctly. For example:
int x = 5;
- Variable name spelling error: If we use an undeclared variable name (misspelling) in the code, the compiler will not recognize the variable.
Solution: Check whether the variable names in the code are spelled correctly and correct the errors.
int num = 10; cout << nums << endl; // 正確的變量名是num,不是nums
- Variable scope problem: When the variable we reference exceeds its scope, the compiler will report an error. For example:
void func() { int x = 5; } int main() { cout << x << endl; // x在函數(shù)func的作用域內(nèi),無法在main函數(shù)中引用 return 0; }
Solution: Place the variable declaration in the appropriate scope.
Case 2: Using the wrong grammatical structure
When we use the wrong grammatical structure in the C code, the compiler will report the error 'expected primary-expression before ';' token '. This usually occurs in the following situations:
- Wrong expression: When we use wrong expressions in if, for, while and other statements, the compiler will report an error.
Solution: Check whether the expressions in the code are correct and correct the errors.
- Incorrect member access: When we use the dot operator to access an undefined object or use the accessor '->' to access a non-pointer variable, the compiler will report an error.
Solution: Check whether the member access operation in the code is correct and correct the error.
Here is a simple code example that demonstrates how to solve the C syntax error 'expected primary-expression before ';' token':
#include <iostream> using namespace std; int main() { int num = 10; cout << num << endl; return 0; }
In the above code, we have declared the variables correctly The type of num and initialized before using the variable. Therefore, the compiler will not issue an error.
Summary:
When writing C code, we often encounter various syntax errors. When the 'expected primary-expression before ';' token' error occurs, we need to carefully check the code to find out and solve the cause of the error. This article provides two common error conditions and corresponding solutions, hoping to help readers solve this error. At the same time, it is recommended to maintain good coding style and specifications when coding, which can effectively reduce the occurrence of grammatical errors.
The above is the detailed content of How to solve C++ syntax error: 'expected primary-expression before ';' token'?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

People who study Python transfer to C The most direct confusion is: Why can't you write like Python? Because C, although the syntax is more complex, provides underlying control capabilities and performance advantages. 1. In terms of syntax structure, C uses curly braces {} instead of indentation to organize code blocks, and variable types must be explicitly declared; 2. In terms of type system and memory management, C does not have an automatic garbage collection mechanism, and needs to manually manage memory and pay attention to releasing resources. RAII technology can assist resource management; 3. In functions and class definitions, C needs to explicitly access modifiers, constructors and destructors, and supports advanced functions such as operator overloading; 4. In terms of standard libraries, STL provides powerful containers and algorithms, but needs to adapt to generic programming ideas; 5

C STL is a set of general template classes and functions, including core components such as containers, algorithms, and iterators. Containers such as vector, list, map, and set are used to store data. Vector supports random access, which is suitable for frequent reading; list insertion and deletion are efficient but accessed slowly; map and set are based on red and black trees, and automatic sorting is suitable for fast searches. Algorithms such as sort, find, copy, transform, and accumulate are commonly used to encapsulate them, and they act on the iterator range of the container. The iterator acts as a bridge connecting containers to algorithms, supporting traversal and accessing elements. Other components include function objects, adapters, allocators, which are used to customize logic, change behavior, and memory management. STL simplifies C

In C, cin and cout are used for console input and output. 1. Use cout to read the input, pay attention to type matching problems, and stop encountering spaces; 3. Use getline(cin, str) when reading strings containing spaces; 4. When using cin and getline, you need to clean the remaining characters in the buffer; 5. When entering incorrectly, you need to call cin.clear() and cin.ignore() to deal with exception status. Master these key points and write stable console programs.

InheritanceinC allowsaderivedclasstoinheritpropertiesandbehaviorsfromabaseclasstopromotecodereuseandreduceduplication.Forexample,classeslikeEnemyandPlayercaninheritsharedfunctionalitysuchashealthandmovementfromabaseCharacterclass.C supportssingle,m

FunctionhidinginC occurswhenaderivedclassdefinesafunctionwiththesamenameasabaseclassfunction,makingthebaseversioninaccessiblethroughthederivedclass.Thishappenswhenthebasefunctionisn’tvirtualorsignaturesdon’tmatchforoverriding,andnousingdeclarationis

volatile tells the compiler that the value of the variable may change at any time, preventing the compiler from optimizing access. 1. Used for hardware registers, signal handlers, or shared variables between threads (but modern C recommends std::atomic). 2. Each access is directly read and write memory instead of cached to registers. 3. It does not provide atomicity or thread safety, and only ensures that the compiler does not optimize read and write. 4. Constantly, the two are sometimes used in combination to represent read-only but externally modifyable variables. 5. It cannot replace mutexes or atomic operations, and excessive use will affect performance.

There are mainly the following methods to obtain stack traces in C: 1. Use backtrace and backtrace_symbols functions on Linux platform. By including obtaining the call stack and printing symbol information, the -rdynamic parameter needs to be added when compiling; 2. Use CaptureStackBackTrace function on Windows platform, and you need to link DbgHelp.lib and rely on PDB file to parse the function name; 3. Use third-party libraries such as GoogleBreakpad or Boost.Stacktrace to cross-platform and simplify stack capture operations; 4. In exception handling, combine the above methods to automatically output stack information in catch blocks

To call Python code in C, you must first initialize the interpreter, and then you can achieve interaction by executing strings, files, or calling specific functions. 1. Initialize the interpreter with Py_Initialize() and close it with Py_Finalize(); 2. Execute string code or PyRun_SimpleFile with PyRun_SimpleFile; 3. Import modules through PyImport_ImportModule, get the function through PyObject_GetAttrString, construct parameters of Py_BuildValue, call the function and process return
