C program to check if a given string is Keyword or not?

In C programming, a keyword is a predefined or reserved word that has a fixed meaning and is used to perform specific operations. The C language has 32 keywords that cannot be used as variable names or identifiers.

Syntax

int strcmp(const char *str1, const char *str2);

We can check if a string is a keyword by comparing it with all C keywords using the strcmp() function.

C Keywords

The following table lists all 32 keywords in the C programming language −

Example: Checking if String is a Keyword

The following program demonstrates how to check if a given string is a C keyword or not −

#include <stdio.h>
#include <string.h>

int main() {
    char keyword[32][10] = {
        "auto", "double", "int", "struct", "break", "else", "long",
        "switch", "case", "enum", "register", "typedef", "char",
        "extern", "return", "union", "const", "float", "short",
        "unsigned", "continue", "for", "signed", "void", "default",
        "goto", "sizeof", "volatile", "do", "if", "static", "while"
    };
    
    char str[] = "for";
    int flag = 0, i;
    
    for(i = 0; i < 32; i++) {
        if(strcmp(str, keyword[i]) == 0) {
            flag = 1;
            break;
        }
    }
    
    if(flag == 1)
        printf("%s is a keyword
", str);
    else
        printf("%s is not a keyword
", str);
    
    return 0;
}

for is a keyword

How It Works

• We store all 32 C keywords in a 2D character array.
• We use the strcmp() function to compare the input string with each keyword.
• If a match is found, we set a flag and break out of the loop.
• Based on the flag value, we determine if the string is a keyword or not.

Conclusion

This program effectively checks if a given string matches any of the 32 C keywords using string comparison. The approach is simple and works by iterating through all keywords and comparing them with the input string.