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# C Library Function - isupper() [ C Standard Library - ](#) ## Description The C library function **int isupper(int c)** checks whether the passed character is an uppercase letter. ## Declaration Here is the declaration for the isupper() function. int isupper(int c); ## Parameters * **c** -- This is the character to be checked. ## Return Value If c is an uppercase letter, the function returns a non-zero value (true), otherwise it returns 0 (false). ## Example The following example demonstrates the usage of the isupper() function. #include #include int main(){ int var1 = 'M'; int var2 = 'm'; int var3 = '3'; if( isupper(var1) ) { printf("var1 = |%c| is an uppercase lettern", var1 ); } else { printf("var1 = |%c| is not an uppercase lettern", var1 ); } if( isupper(var2) ) { printf("var2 = |%c| is an uppercase lettern", var2 ); } else { printf("var2 = |%c| is not an uppercase lettern", var2 ); } if( isupper(var3) ) { printf("var3 = |%c| is an uppercase lettern", var3 ); } else { printf("var3 = |%c| is not an uppercase lettern", var3 ); } return(0);} Let us compile and run the above program that will produce the following result: var1 = |M| is an uppercase letter var2 = |m| is not an uppercase letter var3 = |3| is not an uppercase letter [ C Standard Library - ](#)